1. Field of the Invention
This invention relates to fluid pressure sensing pitot tubes used to operate pressure actuated speedometers on high speed water going vehicles, such as power boats.
2. Description of the Prior Art
Pitot tubes are currently used in measuring the velocity of an object, such as a high-powered speed boat, with respect to the water the boat is moving through. A pitot tube having a forward facing pressure sensing opening is typically attached to the hull of the boat at a point, such as a lower portion of the transom, to maintain the sensing opening substantially beneath the water during foward movement of the boat, including during high speed operating conditions in which the boat is planing or skimming across the surface of the water. The pressure exerted by the water is imposed on the forward facing sensing opening.
Connected to the pitot tube is a pressure operated speedometer which is in fluid pressure receiving communication with the sensing opening. Upon forward movement of the boat pressure exerted on the sensing opening is transmitted to the pressure actuated speedometer. The speedometer is calibrated to translate the received pressure, which is substantially directly proportional to the speed of the boat, into standard speed indicating units, such as miles per hour or knots per hour, to provide an indication of the speed of the boat.
One type of prior art pitot tube for boats consists of a mounting plate with the sensing tube welded directly to the plate. The plate is typically affixed to the transom of a boat using fasteners, such as screws. Once mounted on a boat the tube cannot be readily adjusted up or down to place the sensing opening in an optimum vertical position with respect to the boat. Additionally, if the tube is broken or deformed due to impact with an object in the water, the mounting plate and tube must both be replaced.
Other prior art pitot tubes are mountable on separatable mounting brackets. The mounting bracket has a mounting plate affixed to the boat and a tube holder is secured to the mounting plate. The tube may be removed from the holder and replaced without removal of the mounting plate. A pitot tube receiving passage having a circular cross section is provided in the tube holder and the pitot tube is slid longitudinally into the tube receiving passage of the bracket. Such prior art pitot tubes typically have a connection portion and a sensing portion in which the connection portion is circular in cross section to facilitate engagement with a threaded connector and the sensing portion is flattened or elongated in cross section for strength. A clamping arrangement, such as a set screw, is tightened against a peripheral portion of the tube to maintain the tube in the desired position.
The adjustable prior art tube holders can only receive the circular cross section connection portion of the tube. Consequently, the flattened or elongated sensing portion of the tube extends downwardly, or is cantilevered, a substantial distance below the bracket. The portion of the tube having the circular cross section is much weaker than the flattened sensing portion. Thus, such a tube, due to the inherent weakness of the cross sectional portion held by the tube holder, is readily susceptible to being deformed or broken off when it contacts an object in the water. Also, the tube is susceptible to being rotated about its longitudinal axis due to each the passage and the portion of the tube received within the passage having a circular cross section. If the set screw is insufficiently tight, or if the pressure sensing end of the tube contacts an object, the tube may turn in the passage to cause the sensing opening to be turned or deflected from its correct forward facing position. Having the sensing opening facing in an incorrect direction may provide an erroneous speed indication and, also, the fact that the sensing opening is not in its correct position would not be readily evident to, or detectable by, a person on the boat.
In the prior art pitot tubes a resilient connecting tube typically is used to connect an upper or connection end of the tube to the speedometer. A fitting between the pitot tube and connection tube has a first end which is threadedly engaged with the pitot tube and a second end has a resilient tube receiving nipple. An end of the resilient hose is slid longitudinally onto the nipple and maintained engaged with the nipple by a circumferential clamp. Once the initial resilient tube to nipple connection is made it is cumbersome and time consuming to remove the hose from the nipple. Therefore, awkward as it is, the pitot tube is generally disconnected from the resilient hose by holding the threaded fitting and rotating the pitot tube about its longitudinal axis. Changing a pitot tube in this manner can be a tedious, time-consuming task.
Also, prior art marine pitot tube speed indicating systems typically display an exasperating condition known as "needle jump" in which the needle of the pressure operated speedometer wildly waggles to and fro on its pivot mount. This condition is caused by rapid fluctuations in pressure occurring at the sensing opening of the pitot tube. The pressure conveying opening between the sensing opening and the speedometer is typically open or unimpeded throughout its length. Consequently, the fluctuations in pressure which occur at the sensing opening are transmitted directly to the pressure operated speedometer during conditions, such as buffeting, in which a boat is traveling sufficiently fast to skip from wave crest to wave crest, whereby the sensing opening is sporadically or intermittently immersed in and removed from the water.